In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these pattern miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in the mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and a higher energy level) than these excimer lasers, such as extreme ultraviolet radiation (EUV), electron beam (EB), and X-ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, conventionally a chemically amplified composition has been used, which includes a base material component that exhibits changed solubility in a developing solution under the action of acid, and an acid generator component that generates acid upon exposure.
For example, in the case where the developing solution is an alkali developing solution (namely, an alkali developing process), a positive-type chemically amplified resist composition is typically used, which contains a resin component (base resin) that exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component. If the resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator component, and the action of this acid causes an increase in the solubility of the base resin in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. As a result, by performing alkali developing, the unexposed portions remain as a pattern, resulting in the formation of a positive-type pattern.
The base resin uses a resin for which the polarity increases under the action of acid, resulting in an increase in the solubility of the resin in an alkali developing solution, but a decrease in the solubility of the resin within organic solvents. Accordingly, if a solvent developing process that uses a developing solution containing an organic solvent (an organic developing solution) is employed instead of the alkali developing process, then within the exposed portions of the resist film, the solubility in the organic developing solution decreases relatively, meaning that during the solvent developing process, the unexposed portions of the resist film are dissolved in the organic developing solution and removed, whereas the exposed portions remain as a pattern, resulting in the formation of a negative-type resist pattern. This type of solvent developing process that results in the formation of a negative-type resist pattern is sometimes referred to as a negative-type developing process (for example, see Patent Document 1).
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2). Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.
Furthermore, a multitude of compounds have been proposed as the acid generator used in a chemically amplified resist composition, and examples of known acid generators include onium salt acid generators, oxime sulfonate acid generators, diazomethane acid generators, nitrobenzylsulfonate acid generators, iminosulfonate acid generators, and disulfone acid generators. Among these, as the onium salt acid generator, an iodonium salt having an iodonium ion as the cation or a sulfonium salt having a sulfonium ion as the cation is generally used. Further, the anion (acid) that forms the salt with the aforementioned cation is typically a fluorinated alkylsulfonate ion (for example, see Patent Document 3). Furthermore, recently, acid generators having a fluorinated alkylsulfonate ion with an amide structure and a triphenylsulfonium ion have been proposed (for example, see Patent Document 4).
In recent years, resins having an acid-generating group have been proposed as base resins. For example, resin components have been proposed that have both an acid-generating group that generates acid upon exposure and an acid-degradable group that exhibits changed polarity under the action of acid within the same structure (for example, see Patent Documents 5 to 7). These resin components combine the function of an acid generator and the function of a base component, and enable a chemically amplified resist composition to be prepared using only a single component. In other words, when this type of resin component is subjected to exposure, acid is generated from the acid-generating group within the structure, and the action of that acid causes degradation of the acid-degradable group, thereby forming a polar group such as a carboxyl group that causes an increase in the polarity. As a result, when a resin film (resist film) formed using such a resin component is subjected to selective exposure, the polarity of the exposed portions increases, and by performing developing using an alkali developing solution, the exposed portions can be dissolved and removed, thus forming a positive-type resist pattern.